Disc Brake Blues.

[Sunbeem]

Well I woke up this morning --

The right hand front disc, or rotor, on the RS shows a central shiny band, with a hot blue line in the middle.
The other three braking surfaces are fine.
I'd like to understand what's happening here, if anyone can elucidate ...

Sunbeem.

[Kurt in S.A.]

Amazing how that can happen overnight! You have some serious gremlins in England!!

What type of brakes - ATE or Brembo? For ATEs, have you tried the felt marker radial across the disk and seeing what portion of the marker line is rubbed off? You could do that with any brake system.

Any pulling of the brakes while stopping?

Maybe you have a hard spot on the brake pad...

Kurt in S.A.

[Major Softie]

when was the last time you did any brake work on the bike, and what did you do?

[Sunbeem]

ATE Brakes, and they seem to work very well.
The central third of the braking surface shows contact with the pad.
When I had the wheel out a year ago, I cleaned and bled them, and they've never been any trouble.

Is there any more to centralising than just careful reassembly ? I'm not sure if I removed the caliper when bleeding, and if I check the pad, I'd like to get it all back together properly. Do I remember an off-centre spindle ?

Sunbeem.

[Kurt in S.A.]

Do I remember an off-centre spindle ?

Yes, there's an eccentric bolt that is accessed from the bottom...there's a large hex cap that "hides" it...there's a spring inside there as well. The idea is to spin the tire/disk with a felt mark across the disk and then apply the brakes...see how much of the mark is swept off. The bolt needs to be turned so that all of the pad makes even contact with the disk.

Kurt in S.A.

[Sunbeem]

That makes things much clearer, I'll give it a try. Many thanks Kurt.
If that doesn't work, I can check the pad in the knowledge that I can properly realign the caliper when I reassemble.

Sunbeem.

[Ken in Oklahoma]

I'm not a fan of the felt tip pen method of aligning the caliper to the brake disk. I've chased my tail way too many times and spent too much time trying to get it right. The calipers will align themselves if you only let them.

The idea is simple, if not simple to communicate. You remove that cap and spring talked about earlier. Now you find a wrench or socket that you can get onto that nut, 13mm IIRC. The idea is to put some brake pressure on the hand lever and then move the nut to find out where the caliper "wants" to be. Where it wants to be is lying flat against the disk, which is of course what you're aiming for using the felt tip pen technique.

If you don't have a helper to hold the front brake lever you can do as I do and use a rubber band cut from a motorcycle inner tube to keep pressure on the lever. Now you can move the nut, watch the caliper move in response, and determine for yourself where the null position is for the caliper. There is a bit of ambiguity at the null position. I'll move the wrench one way until I feel some resistance and, move it the other way, then split the difference.



Ken

[Sunbeem]

Excellent ... thanks Ken. Sounds like a combination of your method of adjusting, and checking with felt tip, could be a good approach. Thinking back, I reset them like that last time, but without fully realising the accuracy required ...

I suppose the thickness of a felt tip line will be minimal, so if I've worn the centre part of the disc more than the rest, it will show.

Sunbeem.

[Zombie Master]

Excellent ... thanks Ken. Sounds like a combination of your method of adjusting, and checking with felt tip, could be a good approach. Thinking back, I reset them like that last time, but without fully realising the accuracy required ...

I suppose the thickness of a felt tip line will be minimal, so if I've worn the centre part of the disc more than the rest, it will show.

Sunbeem.

Don't for get to clean a lube all the caliper parts. It may have gotten stuck due to corrosion, and there was the hang.

[bbelk]

Well I woke up this morning --

The right hand front disc, or rotor, on the RS shows a central shiny band, with a hot blue line in the middle.
The other three braking surfaces are fine.
I'd like to understand what's happening here, if anyone can elucidate ...

Sunbeem.

Clearly you have one too many disks up there. What you need is a right hand fork that is cleaned up and doesn't have that redundant disk on it. I happen to have one that is free of the extra stuff and I will be happy to send it to me if you will send me that cluttered up right hand fork with the ATE disk mount on it.

Glad to help.
Brad